Why didn't Jack show more interest in Ennis's children? This virtual apathy on Jack's part towards the offspring of his lover and best friend has always puzzled me; I know that I would cherish the children of someone who I loved as much as Jack did Ennis.
Examples: When Ennis brings Jack up to meet Alma, and Jack learns of Ennis's two girls, why didn't he ask to see them? When Jack shows up after the divorce, and Ennis introduces him to his daughters, they make perfunctory hellos, but after Ennis rebuffs Jack (to the pain of both of them), why didn't Jack step back over to the truck and make some charming goodbye to his lover's children? I could imagine him saying something like, "It sure was nice to meet you girls. You keep your old dad out of trouble, hear?"
If nothing else, Jack might have ingratiated himself with Ennis even more by showing more interest in his children, and evincing more sympathy for Ennis's position in regard to them.
Just some thoughts...
Scott